FALL RIVER — State and local police officers swept through Fall River this week, arresting 20 alleged street-level drug dealers accused of selling narcotics to undercover police detectives earlier this summer.

Authorities said they were pursuing an additional 18 suspects who have warrants for their arrest.

On Thursday, the Massachusetts State Police announced that Wednesday’s warrant sweep followed a lengthy investigation by the State Police Gang Unit, the Southeastern Massachusetts Gang Task Force, and the Fall River Police Department Vice and Special Operations Unit.

Mayor Will Flanagan said authorities are “cracking down” on illegal drug dealing in the city.

“We’ve developed a very good network of intelligence at the local, state and federal levels, so working with our partner agencies, we’ve been able to conduct surveillance and infiltrate the drug distribution trade here in the city,” Flanagan said. “We’ll now gather intelligence we’ve gained from these arrests and use it to make more arrests.”

According to court documents, undercover state police detectives, beginning in early June, bought illegal narcotics from alleged drug dealers in several Fall River neighborhoods, including the Flint, the South End and Corky Row.

The undercover detectives drove regular civilian vehicles, wore concealed recording equipment and were monitored by backup surveillance teams of Fall River police and state police detectives, according to police reports.

The undercover detectives, after negotiating transactions with the alleged drug dealers, purchased varying amounts of crack cocaine, heroin, marijuana and prescription pills, according to police reports.

Arrest logs available Thursday at the Fall River Police Department indicated that 21 of 32 total arrests from Wednesday through early Thursday morning were from warrant apprehensions for alleged drug-dealing offenses. The Herald News could not immediately confirm which arrests were related to the joint undercover investigation.

Beginning Wednesday morning, troopers from the State Police Detective Unit for Bristol County and the State Police Violent Fugitive Apprehension Section assisted gang unit troopers and Fall River police officers in arresting the alleged dealers, some of whom have prior drug arrests, according to court documents. A member of the Massachusetts Parole Board also assisted in the citywide drug sweep.

Authorities said the Fall River sweep, along with other recent similar operations in Lawrence and Holyoke, are part of the state police’s “Heroin Initiative” to disrupt illegal drug distribution in Massachusetts. Approximately 20 suspected dealers were arrested in each of the other sweeps, officials said.

Flanagan, a former prosecutor, said law enforcement will continue to crack down on drug dealing in Fall River.

“We’re not just focused on the street-level dealers; our goal and objective is to target the big fish, too,” Flanagan said. “We have a long way to go, and we are committed to keep on going.”